The present disclosure relates generally to photolithography, such as is used in the manufacture of semiconductor integrated circuits.
Photolithography is a mechanism by which a pattern on a mask is projected onto a substrate such as a semiconductor wafer. In areas such as semiconductor photolithography, it has become necessary to create images on the semiconductor wafer which incorporate minimum feature sizes under a resolution limit or critical dimension (CD). Currently, CDs are reaching 65 nanometers and less.
Semiconductor photolithography typically includes the steps of applying a coating of photoresist on a top surface (e.g., a thin film stack) of a semiconductor wafer and exposing the photoresist to a pattern. A post-exposure bake is often performed to allow the exposed photoresist, often a polymer-based substance, to cleave. The cleaved polymer photoresist is then transferred to a developing chamber to remove the exposed polymer, which is soluble to an aqueous developer solution. Typically, a solution such as Tetra-Methyl Ammonium Hydroxide (TMAH) is applied to the resist surface in the form of a puddle. A de-ionized (DI) water rinse is then applied to remove the dissolved photoresist and a spin dry process is used to dry the wafer. The wafer can then be transferred to an additional baking process to remove any moisture on the resist surface or can be transferred to a next process operation. Once dried, only a patterned layer of photoresist exists on the top surface of the wafer.
Several problems often exist after the above described process, especially as advancements in semiconductor technology result in relatively thin (tight pattern density) and/or relatively tall (high aspect ratio) patterned layers of photoresist. One problem is that the photoresist is less solid and easily suffers from bending and/or collapse at development rinsing and drying steps due to excessive capillary forces between adjacent portions of photoresist. Other problems exist due to factors associated with the use of the TMAH, including an extended developing time and shrinkage of the photoresist upon exposure to the TMAH. Furthermore, the pH of TMAH is often not desirable for certain procedures and operations.
One solution that addresses the bending and/or collapse of photoresist is to add supercritical CO2 during the drying process, as disclosed in U.S. Pat. No. 6,656,666 and the article Zhang, et al., “Chemical-Mechanical Photoresist Drying In Supercritical Carbon Dioxide With Hydrocarbon Surfactants,” J. Vac. Sci. Technol. B 22(2) p. 818 (2004), both of which are hereby incorporated by reference. However, this solution adds an additional processing material (the supercritical CO2) to the otherwise conventional process, requires a relatively long period of time, and does not alleviate the adverse effects of the capillary forces throughout the entire process.
It is desired to improve the lithographic process by reducing the effects of the capillary forces and by reducing the amount of steps and/or processing time and material required.